Fuel cell technology shows great promise as an alternative energy source for numerous applications. Fuel cells have been investigated for use in mobile applications, such as portable computers, mobile communications, and GPS tracking devices. Several types of fuel cells have been developed, including polymer electrolyte membrane fuel cells, direct methanol fuel cells, alkaline fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, and solid oxide fuel cells. For a comparison of several fuel cell technologies, see Los Alamos National Laboratory monograph LA-UR-99-3231 entitled Fuel Cells: Green Power by Sharon Thomas and Marcia Zalbowitz.
An important challenge faced in the development of fuel cell technology is providing a constant supply of liquid fuel to the fuel cell system to ensure its continuous and uninterrupted operation. In attempting to improve liquid fuel delivery, previous liquid fuel cell systems have incorporated fuel delivery systems which include fuel bladders, valves, connectors, and vents designed to manage the flow of liquid fuel and equalize the pressure inside the system with the surrounding environment. However, such components increase the complexity of fuel delivery systems, increasing production costs and making the systems more prone to failure. In addition, increasing system complexity decreases design flexibility, making these systems less adaptable to rugged, mobile applications, such as for use in aggressive military environments, where device simplicity and reliability are essential. Furthermore, systems which incorporate multiple valves and venting mechanisms are more cumbersome, often requiring manual operation and additional user resources.
Fuel delivery system designs also must take into account safety concerns, such as the desire to avoid unnecessary exposure to the liquid fuel, and environmental concerns, such as ensuring that potentially hazardous fuels are not unintentionally discharged into the surrounding environment. Consequently, the requirement that fuel be delivered safely and with an acceptably low risk of spillage complicates fuel delivery designs and may lead to inefficiencies. In summary, the need to provide a constant fuel supply while adhering to acceptable safety standards has resulted in increasingly complex fuel delivery systems which are both expensive to produce and cumbersome to operate.